1. Field of the Invention
The present invention relates to a powertrain system for a vehicle, the power train system including a lateral engine, a hydrostatic transmission (hereinafter referred to as “HST”), and a transaxle, the HST including a hydraulic pump and hydraulic motor separated from each other, and the transaxle including the hydraulic motor.
2. Related Art
As disclosed by JP 2006-256510 A, there is a well-known conventional working vehicle, such as a utility vehicle, equipped with a powertrain system including an engine, an HST and a transaxle. The engine is a lateral engine having a lateral engine output shaft (extended in the lateral direction of the vehicle). The HST includes a hydraulic pump and a hydraulic motor fluidly connected to each other via pipes, however, the hydraulic pump is coupled to the engine, and the hydraulic motor is coupled to a transaxle housing of the transaxle, so that the hydraulic pump and the hydraulic motor are separated from each other. The hydraulic pump includes a lateral pump shaft connected coaxially to the engine output shaft, and the hydraulic motor includes a lateral motor shaft connected coaxially to a lateral rotary shaft in the transaxle housing.
The lateral engine is advantageous to minimize the powertrain system in the fore-and-aft direction of the vehicle. The hydraulic motor separated from the hydraulic pump is advantageous to minimize the transaxle including the hydraulic motor. The pipes interposed between the hydraulic pump and the hydraulic motor are flexible so as to increase flexibility in arrangement of the transaxle relative to the engine and in arrangement of other components of the vehicle. Further, such a flexibility in arrangement of components in the vehicle contributes to improvement of steering performance of the vehicle.
However, any portion of the powertrain system between the engine and axles driven by the transaxle may need change in design if either a gasoline engine or a diesel engine should be selected to serve as the engine of the powertrain system, if the vehicle needs to be equipped with an unexpected additional working implement, e.g., a grass mower, or in other cases. The selection of either the gasoline engine or the diesel engine may need selection of whether or not an additional transmission should be assembled in any portion of the powertrain system. If the vehicle needs to be equipped with the additional working implement, an additional power take off (hereinafter referred to as “PTO”) shaft should be arranged in any portion of the powertrain system. The transaxle is mostly required to have a change of design (for example, change of gears in the transaxle casing) to correspond to these cases. Therefore, such a change of design is likely to be drastic so as to increase costs.
Further, in the situation where some latent cases requiring change of design exist, the transaxle (without the hydraulic motor), the hydraulic pump and the hydraulic motor are hindered from being standardized for simplifying and economizing their inventory control and for facilitating their maintenance.